Beckhoff AX8000 servo installation fuse selection

Beckhoff AX8000 Multi Axis Servo System Installation and Fuse Protection Selection Guide

In modern high-precision automated production lines, multi axis synchronous motion control imposes strict requirements on the real-time performance, power density, and modular scalability of servo drive systems. The Beckhoff AX8000 multi axis servo system, with its extremely short EtherCAT cycle time (minimum 62.5 μ s, paired with distributed clock), scalable DC bus design, and flexible safety features (TwinSAFE STO/SS1/Safe Motion), has become the core driving platform for high-end mechanical equipment. However, the reliable operation of the system depends not only on selection calculations, but also on standardized mechanical installation, precise DC bus capacitor matching, UL/CE compliant fuse protection selection, and compliance understanding of Dual Use export control clauses. This article will be based on the technical manual of the AX8000 series, and provide an in-depth analysis of the full stack technical points of the system, including hardware architecture, installation specifications, power/ground/fuse protection design, and preventive maintenance.

Chapter 1: Product Architecture and Selection Overview

1.1 Modular hardware system

The AX8000 adopts a modular combination structure, with all modules having a width of 60mm or 90mm and a uniform height of 230mm. It can be quickly connected to the DC bus, 24V control power, and EtherCAT bus through AX Bridge without tools.

Core module type:

Power module (AX86xx): converts single-phase/three-phase AC or DC power into a stable DC bus voltage (up to 848 VDC).

AX8600: DC input (560/640 VDC), 50 A, suitable for pure DC bus power supply scenarios.

AX8620: Single phase 100-240 VAC or three-phase 200-480 VAC, 20 A, built-in C3 class filter.

AX8640: Three phase 200-480 VAC, 40 A, suitable for high-power drive groups.

Axis module (AX81x8 single axis/AX8206 dual axis):

AX8108: 8 A/4 A (8/16 kHz switching frequency), narrow module (60mm).

AX8118：18 A / 9 A， Wide module (90mm).

AX8128：28 A / 14 A， Wide module (90mm).

AX8206: Dual axis, 6 A per axis, narrow module (60mm), supports two channels to connect motors of different powers.

Combination module (AX85xx): Integrating the power module with the single axis module to save cabinet space.

AX8525:25 A-axis current+50 A DC bus output.

AX8540:40 A-axis current+80 A DC bus output.

Capacitor module (AX8810): expands the DC bus capacitor (1755 μ F), absorbs braking feedback energy, and reduces braking resistance losses.

1.2 TwinSAFE Safety Function Selection

The AX8000 axis module is divided into three sub models according to safety level (distinguished by the b-digit in the model):

B=0: No security function.

B=1: Integrated TwinSAFE STO (Safe Torque Off) and SS1 (Safe Stop 1), triggered through FSoE protocol or hard wired safety input, compliant with SIL 3/PL e.

B=2: Integrated TwinSAFE Safe Motion, supporting up to 17 safety functions (including SLS, SOS, SS2, SLP, SBC, SBT, etc.).

Important constraint: Safety functions require the use of Beckhoff certified motor feedback systems (such as EnDat 3 encoders with SIL2 or SIL3 capabilities for OCT). If a third-party motor is equipped with a safety encoder, the equipment manufacturer must complete FMEDA analysis and EMC testing on their own.

Chapter 2: Mechanical Installation Specifications and Ventilation Requirements

2.1 Installation location and heat dissipation space

The AX8000 must be installed vertically inside the control cabinet, with a ventilation space of no less than 50mm reserved above and below to ensure the forced convection heat dissipation effect of the built-in temperature control fan. The installation base plate should be a conductive and galvanized metal plate to achieve low impedance grounding.

Standard installation process:

Prefabricate M5 threaded holes on the installation plate according to the Beckhoff universal drilling template.

Place the power module on the leftmost side and secure it with M5 × 5 screws (strength grade 8.8) with a torque of 6 Nm.

Arrange the axis modules to the right in sequence, and it is recommended to arrange them from high to low power (such as AX8640 → AX8118 → AX8206 → AX8108) to optimize the DC bus current distribution.

Insert the grounding Hanger onto the grounding bolt of the right module, and then tighten it onto the left grounding bolt of the adjacent module to form a continuous low impedance grounding chain.

2.2 Stacking and Storage Restrictions

Under the original packaging, the stacking height of power/shaft/capacitor modules shall not exceed 8 layers, and the combination module (AX85xx) shall not exceed 3 layers. Long term storage (>5 years) requires the execution of a capacitance forming procedure - power on and no-load operation for 60 minutes to restore the dielectric performance of the DC bus capacitor.

Chapter 3: Electrical Installation and Grounding/EMC Core Points

3.1 Power wiring and fuse protection

The power wiring of AX8000 varies depending on the module type, and it is necessary to strictly distinguish between single-phase/three-phase and DC input:

Key points for module input terminal wiring

AX8620 X01 (10 pins) single-phase to L1/N, three-phase to L1/L2/L3/PE; 24V control power is connected to 24V/GND.

AX8640 X01 (4-pin)+X02 (6-pin) X01 connected to three-phase main power supply, X02 connected to 24V control power and external braking resistor.

AX8600 X01 (7-pin) DC+/DC - connected to DC bus, 24V/GND connected to control power.

AX85xx X01 terminal block (L1/L2/L3/PE) with a maximum wire diameter of 35 mm ² (AWG 2) and a torque of 2.5-4.5 Nm.

Key warning: Before connecting the external braking resistor, the short circuiting piece between Rbint+and Rb on the power module terminal must be removed, otherwise the external braking resistor cannot be correctly switched and the system will report an error and stop. The PE wire of the braking resistor must be connected through the PE point of the X02 terminal.

3.2 Implementation of Separation between Protective Grounding (PE) and Functional Grounding (FE)

The AX8000 has a very strict distinction between grounding:

Protective grounding (PE): Connect a cable with a ring terminal of ≥ 10 mm ² to the central grounding point of the control cabinet mounting board through the grounding bolt on the left side of the power module to prevent electric shock. Optionally, attach a second PE wire to the grounding bolt on the right side of the last module.

Functional Grounding (FE): Low impedance connection between modules is achieved through Grounding Hanger, ensuring effective discharge of high-frequency EMC interference. The fixing nut torque of the grounding hanging ring is 2.7 Nm, and the use of spring washers is strictly prohibited.

EMC rating and cable length:

Only use Beckhoff original shielded motor cables.

When there is no reactor, the maximum length of a single motor cable is 25 meters, and the total length of the system is ≤ 300 meters.

After installing the AX2090-ND80 reactor, a single cable can be extended up to 100 meters, and the total length of the system is ≤ 500 meters.

To meet the C2 EMC limit (residential and light industrial environments), additional AX2090-NF80 series filters need to be installed and matched with corresponding reactors.

3.3 Calculation of DC bus capacitance and charging time

The AX8000 adopts a common DC bus architecture, and the DC bus capacitors of all axis modules are uniformly charged by the power module. The maximum rechargeable capacitance value of the power module when first powered on varies depending on the voltage level:

Power module 230 VAC 400 VAC 480 VAC

AX8620 25,000 μF 8,500 μF 6,000 μF

AX8640 - 13,500 μF -

AX8540 - 23,000 μF 13,000 μF

Engineering example: If the system includes 1 x AX8640 (625 μ F)+10 x AX8206 (10 x 135 μ F=1350 μ F)+1 x AX8810 (1755 μ F), the total capacitance is 3730 μ F, which is lower than the upper limit of 13500 μ F of AX8640 at 400V, the design is safe. The charging time is about 5 × RC. Taking AX8620 full load capacitor (8500 μ F) as an example, the charging time is about 1.4 seconds.

Chapter 4: UL/CE Compliance Fuse Protection Selection Strategy

4.1 Circuit breaking schemes under different SCCR levels

AX8000 requires the selection of external fuses based on the short-circuit current rating (SCCR) of the installation site to comply with UL 508A or IEC 60269 requirements.

CE compliance (gG fuses or C-characteristic circuit breakers):

Maximum SCCR specification for power module fuse

AX8620 gG (A) or C characteristic circuit breaker, ≤ 25 A 5 kA

AX8640 gG (A) or C characteristic circuit breaker, ≤ 50 A 5 kA

AX8525/AX8540 gG (A) or C characteristic circuit breaker, ≤ 100 A 10 kA

UL compliant (Class J fuses):

Use UL certified Class J fuses and strictly follow the replacement rules in section SB4.2.3 of UL 508A.

If a 65 kA SCCR is required, semiconductor fuses (aR type) can be connected in series:

AX8620：Bussmann FWC-32A10F（32 A）

AX8640：Bussmann FWP-63A22F（63 A）

Semiconductor fuses are only used for short-circuit protection and must be connected in series with Class J fuses to achieve line protection.

4.2 Application oriented setting of fuse current

It is not recommended to directly select based on the maximum rated current of the power module, but should be calculated based on the sum of steady-state currents (I ₀) of all servo motors multiplied by the simultaneous coefficient.

Example: In a certain three-axis handling system, the motor currents of each axis are 6.90 A, 1.95 A, and 0.85 A, with a total current of 9.70 A. Taking a simultaneous coefficient of 0.7, the equivalent current is 6.8 A. Therefore, a 10 A fuse can be selected, which is much lower than the upper limit of 25 A of the power module, and is both safe and economical.

Chapter 5: Status Display and Fault Diagnosis

5.1 Interpretation of 7-segment display screen status

AX8000 modules provide real-time feedback on their status through a high brightness 7-segment LED display screen

Power module:

E (green constantly on): EtherCAT master station is active and configured for activation.

P (green flashing): The DC bus is charging and discharging (flash>48V, slow flash ≤ 48V).

P (red): Fault.

Axis module:

A (green constantly on): The shaft is enabled and there are no faults.

A (flashing red and green alternately): The axis is executing a fault response.

S (red): STO triggered (safe shutdown).

Debug firmware: D (flashing green) indicates that the device is currently running a beta firmware and needs to be upgraded to the official version as soon as possible.

5.2 Quick troubleshooting of common faults

Possible causes of malfunction and corresponding measures

The display screen of the power module is not lit, and the 24V control power is missing. Check the 24V/GND wiring of X01/X02 terminals; Confirm that the external 24V power output is normal.

After power on, the DC bus cannot establish the main power supply. If the charging resistor is open circuit, check the three-phase input voltage; Measure whether L1/L2/L3 of X01 terminal is within the allowable range.

The axis module displays red E EtherCAT communication interruption and checks the network cable connection; Confirm that the EtherCAT configuration of the main station is consistent with the actual topology.

Overheating or burning of brake resistor. External brake resistor selection is too small or not switched correctly. Confirm the removal of Rbint+and Rb short connectors; Check if the resistance value is ≥ the minimum allowable value (AX8620 is 33 Ω).

Touch screen/upper computer reports "DC link overvoltage". The braking energy feedback overload increases the power of the braking resistor; Or add AX8810 capacitor module to absorb instantaneous energy.

Chapter 6: Preventive Maintenance and Component Replacement

6.1 Cleaning Standards

It is strictly prohibited to use compressed air for cleaning to prevent dust from entering the interior of equipment with an IP20 protection level.

Allow the use of cloth or brush in conjunction with industrial alcohol or glass cleaner to wipe the surface.

Before cleaning, it is necessary to confirm that the equipment has been completely powered off and the DC bus voltage has dropped to<50V.

6.2 Service life and replacement cycle

All modules of AX8000 are maintenance free, but their peripheral components have a limited lifespan

Fan: Built in temperature controlled fan, its lifespan is affected by environmental temperature. It is recommended to replace it by Beckhoff Service every 7 years or when abnormal noise occurs.

DC bus capacitor: If stored for more than 5 years, it needs to be re formed - energized and unloaded for 60 minutes.

Braking resistor: Depending on the frequency of braking, if surface discoloration or resistance drift is found, it should be replaced immediately.

6.3 Scrap disposal

Metal components (aluminum, copper, steel) are recycled as scrap metal.

Electronic circuit boards and batteries must comply with the WEEE directive and be handed over to professional electronic waste disposal institutions.

Packaging materials (cardboard, wood, foam) shall be classified and recycled according to local regulations.